MistressLegato is absolutely right. The proper and SAFE way to bind (... in my opinion >_>) is Ace bandages (REAL TAPE? o_o;;; I wasn't aware people actually used real tape!) under a sports bra of at least a size too small. The ace bandages keep the boobage down without causing injury to it other than the squashing and making difficult to breathe itself, while the sports bra over it will help keep them in place (since they aren't actually stuck to your body, they WILL slip otherwise after time, especially if you're running around everywhere. Recommended that when you take bathroom breaks, if your costume permits, take your shirt off and redo the bandage again.)
Also works well for those on a budget -- I've used the same two ace bandages for going on five cons now.
ANYWAY. As for my own con injury - eh, nothing much, except the few times I was seriously having trouble breathing because of the heat and the binding. Oh, the lengths I go to for proper crossplay T_T And my costume had long pants and was made of thick material so it was really hot *weep*